|
(11) | EP 2 056 147 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
|
|
| (54) |
OPTICAL FIBER RIBBON BAND AUS OPTISCHEN FASERN RUBAN DE FIBRE OPTIQUE |
|
|
|||||||||||||||||||||||||||||||
| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
TECHNICAL FIELD
BACKGROUND ART
[0002] In recent years, an optical interconnection system using optical fibers for wiring has been attracting attention as a technology for sending a signal in a transmission device. Usually, such optical fibers are used in a form of an optical fiber ribbon. An optical fiber ribbon is formed by arranging in parallel optical fibers, each obtained by forming a fiber coating made of, for example, an ultraviolet curable resin around the circumference of a glass optical fiber, and then integrating the optical fibers with a ribbon coating made of, for example, an ultraviolet curable resin. A conventional optical fiber ribbon used for the optical interconnection system is formed by, for example, arranging in parallel 12 optical fibers, each having an outer diameter of 250 µm and obtained by forming a fiber coating including a primary layer and a secondary layer on the circumference of a glass optical fiber having an outer diameter of, for example, 125 µm, at a pitch of 250 µm and then integrating the optical fibers with a ribbon coating. The conventional fiber ribbon has a thickness of about 300 pm and a width of about 3.1 mm.
[0003] To improve efficiency in installing wiring of this type of optical fibers in a transmission device, techniques for reducing the diameter of an optical fiber and the thickness of an optical fiber ribbon are under development. In addition, there has been an increasing demand for flame resistance as one characteristic of this kind of optical fiber ribbon. For example, Patent Document 1 discloses an optical fiber ribbon coated with a ribbon coating of flame resistant ultraviolet curable resin.
[0005] WO 2006/101204 A1 discloses a light transmitting body containing a plurality of optical fibers which are arranged in a thinned silica optical ribbon having a thickness of 125 µm.
[0007] JP 2005-326567 discloses an optical fiber ribbon having a collective coating with a thickness of 25 µm which is made of for example flame-retardant UV resin.
DISCLOSURE OF INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
[0008] However, if a fiber coating and a ribbon coating are formed thinner to reduce the diameter of an optical fiber and the thickness of an optical fiber ribbon, favorable flame resistance and screening characteristics cannot be obtained.
[0009] The present invention has been achieved to solve the above problems in the conventional technology and it is an object of the present invention to provide a thin optical fiber ribbon capable of achieving favorable flame resistance and screening characteristics.
MEANS FOR SOLVING PROBLEM
[0010] To overcome the problems and achieve the object mentioned above, the present invention provides an optical fiber ribbon according to claim 1.
EFFECT OF THE INVENTION
[0011] According to the present invention, an optical fiber ribbon uses a fiber coating made of a non-flame-resistant ultraviolet curable resin and thus can achieve favorable screening characteristics as well as a small thickness equal to 200 µm or less. In addition, the optical fiber ribbon is coated with a ribbon coating of a flame resistant resin having a thickness equal to 40 µm or more, and thus can achieve favorable flame resistance.
[0012] Furthermore, according to the present invention, an optical fiber ribbon is formed of glass optical fibers each coated with a single layer coating that is made of a non-flame-resistant ultraviolet curable resin. Thus, the optical fiber ribbon can have flame resistance in the optical fibers and achieve preferable screening characteristics as well as a small thickness equal to 200 µm or less. In addition, the optical fiber ribbon is coated with a ribbon coating made of a flame resistant resin such that a total thickness of the flame resistant layer and the ribbon coating is 40 µm or more. Thus, the optical fiber ribbon can achieve favorable flame resistance.
BRIEF DESCRIPTION OF DRAWINGS
[0013]
[Fig. 1] Fig. 1 is a schematic cross section of an optical fiber ribbon according to a first embodiment of the present invention.
[Fig. 2] Fig. 2 is a cross section of an optical fiber shown in Fig. 1.
[Fig. 3] Fig. 3 is a schematic diagram of a refractive-index profile corresponding to the cross section of the optical fiber shown in Fig. 1.
[Fig. 4] Fig. 4 is a schematic cross section of an optical fiber ribbon according to a second embodiment of the present invention.
[Fig. 5] Fig. 5 is a cross section of an optical fiber shown in Fig. 4.
[Fig. 6] Fig. 6 is a diagram for explaining a relation between thicknesses of coatings of the optical fiber ribbon shown in Fig. 4.
[Fig. 7] Fig. 7 is a table of characteristics of optical fibers, characteristics of optical fiber ribbons,
thicknesses of flame resistant coatings, results of flame test and screening test, and evaluations of installation efficiency of optical fiber ribbons of Examples of the present invention and Comparative Examples.EXPLANATIONS OF LETTERS OR NUMERALS
[0014]
10, 20 Optical fiber ribbon
11, 21 Optical fiber
111, 211 Glass optical fiber
111a, 211a Center core
111b Depressed core layer
111c, 211b Cladding layer
112, 212 Fiber coating
12, 22 Ribbon coating
212a Non-flame-resistant layer
212b Flame resistant layer
D1, D2 Width
HI, H2, T1 to T5 Thickness
R11, R12, R21 to R23 Outer diameter
BEST MODE(S) FOR CARRYING OUT THE INVENTION
[0015] Exemplary embodiments of an optical fiber ribbon according to the present invention are explained in detail below with reference to the accompanying drawings. The present invention is not limited to the embodiments.
(First Embodiment)
[0016] Fig. 1 is a schematic cross section of an optical fiber ribbon according to a first embodiment not forming part of the present invention. As shown in Fig. 1, an optical fiber ribbon 10 of the first embodiment is formed by arranging 12 optical fibers 11, each obtained by forming a single layer of fiber coating 112 on the circumference of a glass optical fiber 111, and integrating the optical fibers 11 with a ribbon coating 12.
[0017] Fig. 2 is a cross section of the optical fiber 11 shown in Fig. 1. The glass optical fiber 111 has an outer diameter R11 of 55 µm to 90 µm smaller than that of a typical optical fiber, i.e., 125 µm. In other words, the outer diameter of the glass optical fiber 111 is reduced to the extent that transmission loss does not increase while installation efficiency improves and possibility of damage in the optical fiber due to bending decreases. The glass optical fiber 111 is explained below.
[0018] The fiber coating 112 has a Young's modulus of 40 kgf to 200 kgf, and is made of a non-flame-resistant ultraviolet curable resin not containing flame resistant agent. This protects the glass optical fiber 111 from external damage and prevents microbending loss as well as achieving favorable screening characteristics. Furthermore, because the glass optical fiber 111 has a small diameter and the fiber coating 112 is a single layer coating, a diameter R12 of the optical fiber 11 is smaller than that of the conventional one, which ensures a small thickness of the optical fiber ribbon 10.
[0019] The ribbon coating 12 of the optical fiber ribbon 10 shown in Fig. 1 is made of an ultraviolet curable urethane acrylate resin containing aluminum hydroxide as flame resistant agent, and has a thickness T1 equal to 40 µm or more. Thus, favorable flame resistance can be achieved.
[0020] The optical fiber ribbon 10 has a small thickness HI equal to 300 µm or less. A pitch P1 between the optical fibers 11 is smaller than that of the conventional ones. This increases flexibility of wiring and installation efficiency in a transmission device while allowing the optical fiber ribbon 10 to have a width D1 smaller than that of the conventional one. Thus, space saving can be achieved.
[0022] Fig. 3 is a schematic diagram of a refractive-index profile corresponding to the cross section of the glass optical fiber 111. As shown in Fig. 3, the glass optical fiber 111 includes a center core 111a, a depressed core layer 111b formed around the center core 111a, and a cladding layer 111c formed around the depressed core layer 111b. The depressed core layer 111b has a refractive index lower than that of the center core 111a. The cladding layer 111c has a refractive index lower than that of the center core 111a and higher than that of the depressed core layer 111b. In other words, the glass optical fiber 111 has a W-shaped refractive-index profile.
[0023] The cladding layer 111c is made of pure silica not containing a dopant for adjusting the refractive index. As shown in Fig. 3, provided that Δ1 denotes a refractive index difference of the center core 111a from the cladding layer 111c, α denotes an α value that is a parameter representing a refractive-index distribution of the center core 111a, Δ2 denotes a refractive index difference of the depressed core layer 111b from the cladding layer 111c, a denotes the diameter of the center core 111a, and b denotes the outer diameter of the depressed core layer 111b, Δ1 is 0.8%, α is 8.0, and Δ2 is -0.5%. The diameter a of the center core 111a is 7.2 µm, and the outer diameter b of the depressed core layer 111b is 12.0 µm.
[0024] With the above refractive-index profile, the optical fiber 111 has a mode field diameter of 5.8 µm at a wavelength of 1310 nm of a signal light source used for signal transmission in a transmission device. The optical fiber 11 has a cut-off wavelength of 1238 nm enabling single-mode transmission at a wavelength of 1250 nm. Besides, the optical fiber 11 has a bending loss of 0.6 dB/turn at a wavelength of 1310 nm when bent with a curvature radius of 1 mm, and a chromatic dispersion value of 1.04 ps/nm/km at a wavelength of 1310 nm. Thus, the optical fiber 11 can be preferably used for an optical fiber ribbon having a small bending loss and high installation efficiency.
[0025] The cut-off wavelength in this description is a fiber cut-off wavelength λc defined by ITU-T G.650.1. Unless otherwise specified, other terms in the description also follow definition and measuring method defined by ITU-T G.650.1.
[0026] The refractive index differences Δ1 and Δ2 are defined, respectively, by Equations (1) and (2):
[0027] In Equations (1) and (2), nc1 is a maximum refractive index of the center core 111a, nc2 is a minimum refractive index of the depressed core layer 111b, and nc is a refractive index of the cladding layer 111c.
[0028] In the W-shaped refractive-index profile, the diameter a of the center core 111a is determined so that a refractive index at the border between the center core 111a and the depressed core layer 111b is equal to that of the cladding layer 111c, and the outer diameter b of the depressed core layer 111b is determined so that a refractive index difference at the border between the depressed core layer 111b and the cladding layer 111c is half the refractive index difference Δ2.
[0030] In Equation (3), r is a position in a radial direction from the center of the optical fiber, n(r) is a refractive index at the position r, and a symbol "^" denotes exponentiation.
[0031] The optical fiber ribbon of the first embodiment is manufactured in the following manner. First, a preform, which is mainly made of fused silica, is drawn by heating and melting it in a drawing furnace to obtain a fused-silica optical fiber. The fused-silica optical fiber is then coated with a liquid ultraviolet curable resin using coating dies. The ultraviolet curable resin is irradiated with ultraviolet rays and cured to form a fiber coating. Thus, an optical fiber is manufactured. Subsequently, 12 optical fibers thus manufactured are arranged in parallel and integrated by applying at the same time with a liquid ultraviolet curable urethane acrylate resin containing aluminum hydroxide. The applied resin is irradiated with ultraviolet rays and cured to form a ribbon coating. Thus, the optical fiber ribbon is obtained.
[0032] As explained above, according to the first embodiment, the fiber coating 112 is made of non-flame-resistant ultraviolet curable resin. Thus, favorable screening characteristics can be achieved while the optical fiber ribbon 10 has a small thickness HI equal to 300 µm or less. In addition, the ribbon coating 12 has a thickness T1 equal to 40 µm or more and is made of flame resistant ultraviolet curable urethane acrylate resin containing aluminum hydroxide, which achieves favorable flame resistance. Although the glass optical fiber having a W-shaped refractive-index profile is described, by way of example and without limitation, in the first embodiment, a different type of optical fiber having a different refractive-index profile can also be adopted such as an optical fiber having a step-type profile or a multimode optical fiber.
(Second Embodiment)
[0033] An optical fiber ribbon according to a second embodiment not forming part of the present invention is explained below. Fig. 4 is a schematic cross section of the optical fiber ribbon according to the second embodiment of the present invention. As shown in Fig. 4, an optical fiber ribbon 20 of the second embodiment is formed by arranging in parallel 12 optical fibers 21, each obtained by forming a fiber coating 212 on the circumference of a glass optical fiber 211, and by integrating the optical fibers 21 with a ribbon coating 22.
[0034] Fig. 5 is a cross section of the optical fiber 21 shown in Fig. 4. As with the optical fiber 11 of the first embodiment, the optical fiber 21 is obtained by forming the fiber coating 212 on the circumference of the glass optical fiber 211. The glass optical fiber 211 includes a center core 211a and a cladding layer 211b formed around the center core 211a, and is a single mode optical fiber having a normal step-type refractive-index profile. An outer diameter R21 of the glass optical fiber 211 is 125 µm.
[0035] The fiber coating 212 includes a non-flame-resistant layer 212a and a flame resistant layer 212b. The non-flame-resistant layer 212a adjacent to the glass optical fiber 211 has a Young's modulus of 40 kgf to 200 kgf, and is made of a non-flame-resistant ultraviolet curable urethane acrylate resin containing aluminum hydroxide as flame resistant agent. This protects the glass optical fiber 211 from external damage and enhances flame resistance of the optical fiber ribbon 20.
[0036] Fig. 6 is an enlarged view of part of the optical fiber ribbon 20 shown in Fig. 4 for explaining the thickness of the coatings thereof. As shown in Fig. 6, a thickness T3 of the fiber coating 212, i.e., a total thickness of the flame resistant layer 212b and the flame resistant layer 212b, is equal to 30 µm or more. Therefore, even if aluminum hydroxide coagulates into clumps in the manufacturing process, such clumps do not damage a surface of the glass optical fiber 211. Thus, the optical fiber 21 can achieve favorable screening characteristics. An outer diameter R22 of the non-flame-resistant layer 212a is 195 µm and an outer diameter of the non-flame-resistant layer 212a, i.e., an outer diameter R23 of the optical fiber 21, is 250 µm.
[0037] The ribbon coating 22 of the optical fiber ribbon 20 shown in Fig. 4 is made of an ultraviolet curable urethane acrylate resin containing aluminum hydroxide as flame resistant agent. A total thickness T5 of a thickness T2 of the ribbon coating 22 and a thickness T4 of the flame resistant layer 212b shown in Fig. 6 is equal to 40 µm or more. Thus, even if each of the ribbon coating 22 and the flame resistant layer 212b has a thickness smaller than 40 µm, the optical fiber ribbon 20 can achieve favorable flame resistance.
[0038] The optical fiber ribbon 20 has a small thickness H2 equal to 40 µm or less. A pitch P2 between the optical fibers 21 is 250 µm and a width D2 of the optical fiber ribbon 20 is equal to that of a conventional optical fiber ribbon. Thus, it is possible to maintain compatibility with the conventional fiber ribbon as well as to increase flexibility of wiring and installation efficiency in a transmission device. Thus, space saving can be achieved.
[0039] The optical fiber ribbon of the second embodiment can be manufactured in the same manner as previously explained for the optical fiber ribbon of the first embodiment except for a process for forming the non-flame-resistant layer and the flame resistant layer.
[0040] As explained above, according to the second embodiment, the optical fiber ribbon 20 has the small thickness H2 equal to 300 µm or less. The fiber coating 212 has the thickness T3 equal to 30 µm or more and includes the non-flame-resistant layer 212a adjacent to the glass optical fiber 211 and the flame resistant layer 212b formed as an outermost layer thereof. Thus, the optical fiber ribbon 20 can achieve favorable screening characteristics while having the flame resistant layer 212b in the fiber coating 212. In addition, the ribbon coating 22 is made of a flame resistant resin and the total thickness T5 of the flame resistant layer 212b and the ribbon coating 22 is equal to 40 µm or more. Thus, favorable flame resistance can be achieved.
[0041] Although the glass optical fiber having the step-type refractive-index profile is described, by way of example and without limitation, in the second embodiment, a different type of optical fiber having a different refractive-index profile can be adopted such as a multimode optical fiber.
[0042] (Examples 1 to 3, Comparative Examples 1 to 4) Optical fiber ribbons were manufactured as Examples 1 to 2 of the present invention, Example 3 not forming part of the present invention and Comparative Examples 1 to 4. Fig. 7 is a table of characteristics of optical fibers, characteristics of the optical fiber ribbons, thicknesses of flame resistant coatings, results of flame redundancy test and screening test, and evaluations on installation efficiency of the optical fiber ribbons of Examples and Comparative Examples.
[0043] In Fig. 7, a single-layer fiber coating of the optical fiber ribbons of Examples 1 and 2 are represented as "SECONDARY", and non-flame-resistant layers and flame resistant layers of the fiber coatings of Example 3 and Comparative Examples 1 to 4 are respectively represented as "PRIMARY" and "SECONDARY". In addition, "UV" represents a non-flame-resistant ultraviolet resin and "FLAME RESISTANT" represents a flame resistant ultraviolet curable urethane acrylate resin containing aluminum hydroxide. The resin used for "PRIMARY" has a Young's modulus of 0.15 kgf to 0.2 kgf, and the resin used for "SECONDARY" has a Young's modulus of 40 kgf to 200 kgf. Besides, "TOTAL THICKNESS OF FLAME RETATDANT COATINGS" represents the thickness of "RIBBON COATING" of Examples 1 and 2 and Comparative Examples 2 to 4 and a total thickness of "SECONDARY" and "RIBBON COATING" of Example 3 and Comparative Example 1.
[0044] A flame test represented as "FLAME RESISTANCE" was conducted under UL1581-1080 (VW-1) standard. Results of the flame test performed on the optical fiber ribbon are represented as "FLAME RESISTANT" indicating that the optical fiber ribbon did not flame or "NON-FLAME-RESISTANT" indicating that the optical fiber flamed. A screening test represented as "SCREENING" was conducted on an optical fiber under the condition of a screening strain of 1%. Results of the screening test are represented as "FAVORABLE" indicating that an excellent optical fiber having a length equal to 1000 m or more was obtained or "UNFAVORABLE" indicating that an excellent optical fiber having a length equal to 1000 m or more was not obtained due to breakage. Regarding installation efficiency, "FAVORABLE" represents that the thickness of the optical fiber ribbon was 300 µm or less and "UNFAVORABLE" represents that the thickness of the optical fiber ribbon was more than 300 µm.
[0045] The optical fiber of Example 1 was the same as the one described in the first embodiment, and the optical fiber of Example 2 had the same W-shaped refractive-index profile as that of the first embodiment, i.e., Δ1 was 0.9%, α was 8.0, Δ2 was -0.5%, a was 6.7 µm, and b was 11.2 µm. The optical fiber was characterized in that a mode field diameter at a wavelength of 1310 nm was 5.5 µm, a cut-off wavelength was 1236 nm, a bending loss at a wavelength of 1310 nm when the optical fiber is bent with a curvature radius of 1 mm was 0.3 dB/turn, a chromatic dispersion value was 0.25 ps/nm/km. Furthermore, the optical fiber of Example 3 was a single mode optical fiber having the same normal step-type refractive-index profile as that of the second embodiment.
[0046] On the other hand, the optical fibers of Comparative Examples 1 and 2 each had the same W-shaped refractive-index profile as that of the first embodiment, in which Δ1 is 1.2% and α is 1.5, Δ2 is -0.2%, a is 7.8 µm, and b is 14.5 µm. The optical fiber was characterized in that a mode field diameter at a wavelength of 1310 nm was 5.5 µm, a cut-off wavelength was 1244 nm, a bending loss at a wavelength of 1310 nm when the optical fiber is bent with a curvature radius of 1 mm was 0.6 dB/turn, a chromatic dispersion value was -7.4 ps/nm/km. Furthermore, the optical fibers of Comparative Examples 3 and 4 each were a single mode optical fiber having the same normal step-type refractive-index profile as that of the second embodiment.
[0047] As shown in Fig. 7, the optical fiber ribbons of Examples 1 and 2 achieved favorable screening characteristics with the optical fiber that was coated with a fiber coating made of only "UV" and that was excellent as having a length equal to 1000 m or more. In addition, the flame resistant coating had a thickness of 50 µm, i.e., more than 40 µm, and thus, the optical fiber ribbons did not flame and represented favorable flame resistance. The optical fiber ribbons each had a small thickness of 200 µm in consideration of space saving and increase in transmission loss due to the thinner coating. In other words, the thickness was sufficiently small, and installation efficiency was favorable. In addition, the pitches between the optical fibers of Examples 1 and 2 were 100 µm and 125 µm, respectively. Thus, the widths of the optical fiber ribbons were about half of that of a conventional optical fiber ribbon, which significantly increases flexibility.
[0048] The optical fiber ribbon of Example 3 achieved favorable screening characteristics with the optical fiber that was coated with a fiber coating that had a thickness of 62.5 µm, i.e., equal to 30 µm or more, while made of "UV" and "FLAME RESISTANT" and that was excellent as having a length of 1000 m or more. Although the ribbon coating had a thickness of 25 µm, "SECONDARY", i.e., the flame resistant layer, had a thickness of 27. 5 µm, and thus, the total thickness of the flame resistant coatings is 52.5 µm, i.e., equal to 40 µm or more. Thus, the optical fiber ribbon did not flame in the flame test and represented favorable flame resistance. In addition, the optical fiber ribbon had a thickness of 300 µm and favorable installation efficiency was achieved.
[0049] In the case of the optical fiber ribbon of Comparative Example 1, the optical fiber broke before the length thereof reached 1000 m in the screening test. The optical fiber ribbons of Comparative Examples 2 and 3 flamed in the flame test. The optical fiber ribbon of Comparative Example 4 had a thickness more than 300 µm and had unfavorable installation efficiency.
[0050] If the optical fiber of Example 1 has an outer diameter of 55 µm and the fiber coating has a thickness of 10 µm, a pitch between the optical fibers can be reduced to 75 µm, which further reduces the width of the optical fiber ribbon, and thus increases flexibility and installation efficiency of the optical fiber ribbon.
[0051] In the above embodiments, an ultraviolet curable urethane acrylate resin containing aluminum hydroxide is used as a flame resistant resin. Alternatively, an ultraviolet curable urethane acrylate resin containing aluminum magnesium hydroxide can be used.
[0052] If the fiber coating of each of the embodiments is a single layer coating, it is preferable that the optical fiber have a bending loss of 1 dB/turn or less at a wave length of 1310 nm when bent with a curvature radius of 1 mm. In consideration of connection with another optical fiber, it is preferable that a mold field diameter at a wavelength of 1310 nm be 5.4 µm or more. An optical fiber having the above characteristics can be achieved with, for example, a silica optical fiber having a W-shaped refractive-index profile, in which Δ1 is equal to 0.8% or more, α is equal to 1.5 or more, and Δ2 is equal to -0.2% or less.
INDUSTRIAL APPLICABILITY
1. An optical fiber ribbon (10) comprising:
a plurality of optical fibers (11) that are arranged in parallel, each optical fiber (11) including a glass optical fiber (111) coated with a fiber coating (112); and
a ribbon coating (12) that coats the optical fibers (11) arranged in parallel, wherein
the optical fiber ribbon (10) has a thickness equal to 200 µm or less,
the glass optical fiber (111) has an outer diameter of 55 µm to 90 µm,
the fiber coating (112) is a single layer coating and is made of a non-flame-resistant ultraviolet curable resin, and
the ribbon coating (12) has a thickness equal to 40 µm or more and is made of a flame resistant resin.
1. Optisches Faserband (10), umfassend:
eine Vielzahl von optischen Fasern (11), die parallel angeordnet sind, wobei jede optische Faser (11) eine optische Glasfaser (111) umfasst, die mit einer Faserbeschichtung (112) beschichtet ist; und
eine Bandbeschichtung (12), die die optischen Fasern (11) beschichtet, die parallel angeordnet sind, wobei
das optische Faserband (10) eine Dicke gleich 200 µm oder weniger hat,
die optische Glasfaser (111) einen Außendurchmesser von 55 µm bis 90 µm hat,
die Faserbeschichtung (112) eine Einzelschicht-Beschichtung ist und aus einem nicht flammfesten Ultraviolett-härtbarem Harz hergestellt ist, und
die Bandbeschichtung (12) eine Dicke gleich 40 µm oder mehr hat und aus einem flammfesten Harz hergestellt ist.
1. Ruban à fibres optiques (10) comprenant :
une pluralité de fibres optiques (11) qui sont agencées en parallèle, chaque fibre optique (11) comprenant une fibre optique de verre (111) recouverte d'un revêtement de fibre (112) ; et
un revêtement de ruban (12) qui recouvre les fibres optiques (11) agencées en parallèle, le ruban de fibre optique (10) présentant une épaisseur égale à 200 µm ou moins,
la fibre optique de verre (111) présentant un diamètre externe de 55 µm à 90 µm,
le revêtement de fibre (112) étant un revêtement monocouche et étant constitué de résine durcissable par ultraviolets non ignifuge, et
le revêtement de ruban (12) présentant une épaisseur égale à 40 µm ou plus et étant constitué de résine ignifuge.
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.
Patent documents cited in the description